1. Field of the Invention
The present invention relates to a method used in a wireless communications system and related communication device, and more particularly, to a method of handling resource assignment in a wireless communications system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) for communicating with a plurality of user equipments (UEs) and communicates with a core network including a mobility management entity (MME), serving gateway, etc for NAS (Non Access Stratum) control. A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system, with carrier aggregation and relay deployment. The carrier aggregation, where two or more component carriers are aggregated, allows a UE of the LTE-A system to simultaneously transmit and receive data via multiple carriers, where the UE of the LTE system can only utilize one carrier for data transmission at any time.
In the LTE system, resource assignment can be achieved by a physical downlink control channel (PDCCH) used to carry a message known as Downlink Control Information (DCI) with certain DCI format. The PDCCH message includes resource assignment and other control information, e.g. a transmission power control (TPC) command, a downlink assignment including a physical downlink shared channel (PDSCH) related information, and a uplink grant including a physical uplink shared channel (PUSCH) related information, for a UE or group of UEs. The downlink assignment is downlink resource assignment, whereas the uplink grant is uplink resource assignment.
In the LTE-A system, how to allocate a PDCCH for a UE when the network configures the UE to use multiple component carriers (carrier aggregation) has not been considered. To follow the LTE system a scheme that one PDCCH on one component carrier may be adopted. However, such allocation wastes PDCCH resources because each component carrier has to be assigned one PDCCH. Besides, the UE has to receive PDCCH on each component carrier. This means the UE has to turn on its receiver for receiving PDCCH signaling on each component carrier and thereby wastes UE power.